Repairing damaged bakelite/plastic parts

I measured the arc of the missing section and then dammed off a slightly larger section from the good part of the surround. I used tape, but you could use clay. I sprayed the area with silicon to keep the epoxy from sticking. I then filled the dam with the epoxy, which mixes itself in the injection tube. Next day, I took off the hardened epoxy, which is now my mold, and used it to backup the missing section. I turned the surround upside down and filled it with more epoxy.

Here is the repaired surround in primer. I used some fiberglass screen, like goes into your windows of your house, and embedded it in the back side of the epoxy for added strength.